1. Field of the Invention
The present invention relates to a field emission device and a method of operating the same, and more particularly, to a field emission device enabling rapid pulse operation and a method of operating the same.
2. Discussion of Related Art
A field emission device emits electrons from a cathode electrode by applying an electric field in a vacuum atmosphere, and is used as a field emission display (FED), a field emission lamp (FEL), a field emission X-ray, etc.
Such field emission devices are classified into diode field emission devices composed of a cathode electrode and an anode electrode and triode field emission devices composed of a cathode electrode, an anode electrode and a gate electrode. Here, the diode field emission device emits electrons due to a voltage difference between the cathode electrode and the anode electrode, whereas the triode field emission device emits electrons due to induction by the gate electrode.
Hereinafter, the structure and operating method of a conventional field emission device will be described with reference to the drawings.
FIG. 1 is a diagram showing a structure of a conventional field emission device, particularly, a triode field emission device.
As shown in FIG. 1, the conventional triode field emission device includes a lower substrate 100, and a cathode electrode 110 formed on the lower substrate 100 and including a plurality of field emission sources 120. Here, the cathode electrode 110 has a gap 111 to insulate pixels or blocks from each other. A gate electrode 130 is provided on the cathode electrode 110 to induce field emission, and an insulating layer or spacer (not shown) is interposed between the cathode electrode 110 and the gate electrode 130.
Further, an upper substrate 140 disposed parallel to the lower substrate 100 and an anode electrode 150 formed on a bottom surface of the upper substrate 140 to face the cathode electrode 110 are provided.
An anode power source 160 providing a DC voltage to the anode electrode 150 and a gate power source 170 providing a DC voltage to the gate electrode 130 are also provided.
A current controller 180 controlling field emission current flowing through the cathode electrode 110 is provided, which may be implemented using a MOSFET.
In the field emission device having such a structure, the gate electrode 130 induces electron emission from the field emission source 120, and the emitted electrons are accelerated in a direction of the anode electrode 150. Particularly, the field emission device is operated by a current driving method, which will be described in detail below.
The field emission device is operated by a current driving method in which the current controller 180 controls field emission current flowing through the cathode electrode 110 so that field emission occurs in a specific pixel or block, in a state in which a uniform DC voltage is applied to the anode electrode 150 and the gate electrode 130 by the anode power source 160 and the gate power source 170.
Specifically, when the current controller 180 is turned on, the cathode electrode 110 is grounded (0 V), a sufficient voltage for field emission is applied to both ends of the gate electrode 130 and the cathode electrode 110, and thus the field emission occurs in a corresponding pixel or block.
When the current controller 180 is turned off, the cathode electrode 110 is electrically separated from the grounded electrode, and thus electrons remaining in the cathode electrode 110 are emitted. Accordingly, a positive potential of the cathode electrode 110 is increased, the field emission is interrupted due to a decreased voltage between the gate electrode 130 and the cathode electrode 110, and an increase in potential of the cathode electrode 110 is stopped.
Such a current driving method may control field emission using a low signal source of 5 V or less capable of turning on/off a MOSFET used as a device for the current controller 180.
FIG. 2 is a timing diagram showing a change in voltage of each electrode during operation of the conventional field emission device. A top graph shows level changes in voltage (Vg) of a gate electrode and a voltage (Vc) of a cathode electrode according to time, and a bottom graph shows a signal pulse (Vs) applied to a current controller, i.e., a gate terminal of the MOSFET. Here, in each graph, the X axis represents time, and the Y axis represents voltage.
As shown in the graphs, when a DC voltage (Vg) is applied to the gate electrode 130, the current controller 180 is turned on/off according to a signal pulse applied thereto.
When the current controller 180 is turned on by applying a high level of pulse, the cathode electrode 110 is grounded and thus electrons are emitted from the field emission source 120. When the current controller 180 is turned off by applying a low level of pulse, the cathode electrode 110 is separated from the grounded electrode so as to increase a voltage, and thus the field emission is interrupted.
While the voltage (Vc) of the cathode electrode is vertically dropped at the time when the current controller 180 is turned on, that is, at a rising edge of the signal pulse (Vs), the voltage of the cathode electrode 110 is gradually increased in a parabolic shape at the time when the current controller 180 is turned off, that is, at a falling edge of the signal pulse (Vs). In other words, since the field emission current cannot be immediately blocked even though the current controller 180 is turned off, it is difficult to implement rapid pulse driving.